The raffinate stream from the first extraction stage of the "PUREX" process (used to recover plutonium and uranium from spent fuel) and the liquid metallic sodium used to cool some nuclear reactors is contaminated with various radioactive isotopes. The raffinate stream is stripped of nitric acid and is a high level waste which consists primarily of nitrates in an aqueous solution. The metallic sodium is converted into stable compounds such as a hydroxide, a salt, or an alkoxide by reacting the sodium with either water, an acid, or an alcohol.
The current practice is to dehydrate the liquid waste by heating, then to consolidate the residue by either calcination or vitrification at high temperatures. The resulting metallic hydroxides can be converted into a vitreous waste form using conventional glass technology.
Unfortunately, because of the high fluxing temperatures (about 1150.degree. C.) which are required to melt the glass, additional off-gassing scrubbing capacity or other absorbent procedures are needed to deal with the volatilization of radionuclides such as iodine, cesium, and ruthenium. These high fluxing temperatures can also shorten the life of the furnace and can create problems with the materials into which the molten glass is cast, such as the sensitization of stainless steel to stress corrosion cracking.